This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/EP00/10678 which has an International filing date of Oct. 30, 2000, which designated the United States of America, the entire contents of which are hereby incorporated by reference.
The invention generally relates to a turbine blade, in particular a gas turbine blade. More preferably, it relates to one having a tip region, a root region and a blade-body region. It may have an inner passage system of individual passages, through which cooling gas can be directed on a flow path inside the turbine blade, and a throttle device influencing the throughflow of the cooling gas. Cooling gas may be directed in the passages from the root region through the blade-body region to the tip region and can be diverted in the opposite direction. Also, it may have outlet openings for discharging the cooling gas from the turbine blade, with these outlet openings being arranged on the outflow side of the turbine blade. The invention may generally relate to a method of producing a turbine blade. In order to achieve a high efficiency during the operation of a turbine with an action fluid, in particular of a gas turbine operated with a gas, the action fluid is heated to a high temperature. In a gas turbine with a combustion chamber for producing the hot gas, the guide and moving blades nearest to the combustion chamber are subjected to a throughflow of cooling gas so that they withstand the high temperatures prevailing there, which are partly above the critical values of the material used for producing the turbine blade. The temperature on and inside the turbine blade is reduced by the cooling gas, so that the mechanical stability and thus the operability of the turbine blade under these conditions are ensured.
In this type of cooling, an outer wall of the turbine blade around which an action fluid flows encloses a meander-shaped passage system which repeatedly directs the cooling gas from a root region up to a tip region of the turbine blade and back again to the root region. The region in which the cooling gas is introduced is designated as leading edge region, and the region in which cooling gas is discharged is designated as trailing edge region. A plurality of outlet openings are provided in the trailing edge region, these outlet openings connecting the passage system of the turbine blade to an exterior space through which the action fluid flows. During operation of the turbine, cooling gas from the passage system of the turbine blade discharges from the openings right onto the surface of the outer wall.
In order to save cooling gas and thereby increase the output of the gas turbine, only as much cooling gas as is absolutely necessary in order to avoid overheating is to be used for the blades. Since many assumptions with regard to various heat transfers are made when designing a blade, these assumptions being construed on the conservative side in order to avoid damage to the blades, and since the actual geometrical configuration of the turbine blades also cannot be established until after the casting is complete, the flow of the cooling gas through the blades is set subsequently, after the casting.
This is normally done by providing leading edge holes or aperture plates in the region of the leading edge for the cooling air entering the turbine blade, these leading edge holes or aperture plates throttling the entry of the cooling gas into the blade. A disadvantage in this case, however, is that these throttling devices have a considerable loss factor and may in addition lead to flow separation in the region of the entry of the cooling gas, so that adequate cooling in this region of the turbine blade cannot be ensured. In addition, this configuration also impairs the leading edge region, in which the pressure difference between first cooling chamber and external hot gas decreases.
An object of an embodiment of the present invention is therefore to design a turbine blade which has a throttle device for setting the throughflow of the cooling gas without influencing the flow of the cooling gas at the leading edge. Another alternative object of an embodiment of the invention is to specify a method of producing such a turbine blade. This method may be simple in terms of design and also being individually adaptable.
An object may also be achieved by the throttle device being arranged upstream of the outlet openings in the rear region of the flow path. By such an arrangement of the throttle device, the throughflow of the cooling gas can be throttled without adverse effects on the flow of the cooling gas. The flow at the leading edge is effected largely undisturbed. The throttling only begins in a rear region of the flow path. The cooling-gas flow has left most of its path behind it and has already fulfilled the tasks of heat dissipation, which are linked with sufficient flow velocity.
The pressure difference between the first cooling chamber and the surrounding hot action fluid is retained, so that no hot gas can enter the blade, a factor which would lead to considerable damage. Reliable cooling of the turbine blade is therefore ensured. At the same time, the consumption of cooling gas is minimized. Only as much cooling gas as is absolutely necessary in order to prevent overheating has to be used. In this way, optimum cooling of the turbine blade and at the same time good efficiency of the turbine are obtained.
Favorable flow control of the cooling-gas flow is possible if the throttle device is attached at a reversing point of a passage. Here, the cross section of the passage and thus the throughflow of the cooling gas can be set to a predetermined degree in a simple manner. Possible dimensional differences which result from the production of the gas turbine can be rendered harmless by the throttle device. Thus the same type of throttle device may also be used on different models of turbine blade. This reduces the number of different components of the turbine blade which are required.
It is especially advantageous if the throttle device is attached at the last reversing point arranged upstream of the outlet openings. At this point, the flow path opens out, so that after that sufficient throttling with high efficiency is no longer possible. At the same time, the cooling gas has a maximum flow path and thus maximum contact with the inner surface of the passage system, a factor which optimizes the cooling effect.
It is especially advantageous if the throttle device is attached in a lead-through opening brought about by the casting process. Lead-through openings, which are produced, for example, by core mounts of the casting core during the casting, can be appropriately utilized in this way. They are normally closed merely by means of plates. The throttle device performs the same closing function and at the same time throttles the cooling-gas flow. By means of this throttle device, it is possible to set the throughflow subsequently and compensate for any possible dimensional inaccuracies after the casting. By utilizing the lead-through openings, production steps can thus be saved, which greatly reduces the production costs.
In order to prevent loss of the throttle device during operation or an undesirable penetration of the throttle device into the passage system, it is advantageous if the lead-through opening is permanently closed by the throttle device. If the throttle device were to be shaken loose and were to get into the passage system, for example during pronounced thermal and mechanical loading of the turbine blade, considerable damage to the turbine blade or complete failure of the cooling could be caused, which would result in breakdown of the turbine within a short time. A throttle device located outside the turbine blade inside the turbine may also cause considerable damage. In addition, the cooling effect would be reduced by the cooling gas being discharged into the environment at an unsuitable point through the lead-through opening, which has been cleared on account of the loss of the throttle device.
It is advantageous if the throttle device is arranged in the root region. As a result, the throttle device can be reached without any problems during inspections of the turbine blade and it is possible to check it for its sealing and throttling effect.
Good stability and operability are provided for if the throttle device is formed by a throttling projection of a plug. In this case, the plug is in each case designed in such a way that it is individually adapted to the outside dimensions of the opening into which it is inserted. This is especially advantageous when the opening is a lead-through opening brought about by the casting process, since its dimensions fluctuate with different models of turbine blade. The throttling is effected by the throttling projection, which fulfills its function even in a very simple construction. The throttling projection can thus be of robust design while ensuring its function, as a result of which the throttle device requires little maintenance and works reliably. The throttling is also reliably ensured at high throughflow rates of the cooling gas and at high associated pressures or greatly fluctuating loads.
Accurate matching of the cooling-gas flow is possible if the throttle device is formed by a foot of a screw calked in a plug. In this case, the screw is inserted into the plug, which is fastened in the lead-through opening. In this way, it is not necessary to make a screw thread in the cast turbine blade. The screw inserted into the plug can be set in an infinitely variable manner and permits individual adaptation of the throttling to the flow requirements of the trailing edge region. The screw is locked in the desired position by the caulking.
Fixed retention is ensured by the plug being welded in place. In this way, the plug, with simple measures, can be accurately fastened and held in the desired position in the opening of the turbine blade, in which it is inserted, without deforming surrounding material for example. The opening may be a lead-through opening brought about by the casting process, but also an opening made in the turbine blade after the casting, for example by drilling. In this case, the location of the throttle device can be better adapted to the model- or casting-dependent requirements.
An object relating to the production of a turbine blade may be achieved in that, after the casting operation, a throttle device influencing the throughflow of the cooling gas is introduced in the rear region of the flow path in such a way as to be arranged upstream of the outlet openings. While the throughflow of the cooling gas is measured, is set up in a lead-through opening brought about by the casting process in such a way that a predetermined value of a throughflow parameter of the cooling gas is achieved, and then the throttle device is fastened permanently in the throttling position.
Due to this procedure, certain cooling-gas throttling still does not have to be taken into account during the casting operation itself. This facilitates the casting operation, simplifies the casting molds and reduces the scrap. An opening brought about by the casting, for example produced by a connection between the casting core and the outer casting shell, this connection holding the core in its position, can be utilized in this way. At the same time, the throttle device closes the lead-through opening. In this way, a work step which is otherwise necessary is saved.
By the subsequent measuring of the throughflow of the cooling gas, the cooling-gas flow can be matched individually and with simple measures to the cooling-gas demand of a turbine blade. The setting is facilitated in this case, since the throttling effect can be influenced from outside in a simple manner. The subsequent fastening of the throttle device in the lead-through opening may likewise be effected from outside. In this case, the fastening, due to the measuring of the cooling-gas flow, can be directly controlled and if need be repeated without damaging the turbine blade.
The production method is very similar for different types of blade if the casting core, during the casting operation, is held in its position relative to the outer casting shell by a guide mount in the root region of the turbine blade, and in that a throttle device is inserted into the lead-through opening brought about by the mount. This facilitates the production process and reduces the conversion time and the number of parts to be used during the production of different types of turbine blade.
An especially simple and easily reproducible production method with low material costs is provided for by the cooling-gas flow being measured in each case after the insertion of plugs having different throttling projections, and by the plug which produces a predetermined throughflow of the cooling gas being welded in place. The throttling projection is also predetermined by the selection of a plug. Thus the plug, by a model measurement, can be more or less the same for turbine blades of the same series. This reduces the production costs, since work steps are simplified or dispensed with.
Individual setting of the cooling-air flow is possible by a plug having a throttle screw, which has a throttling projection projecting into the flow path, being inserted into the lead-through opening brought about by the casting process, and by the throughflow being measured while the screw is adjusted, the screw then being calked in the desired throttling position.
The screwing position can be varied in an infinite manner during the continuous measurement. This permits a very accurate setting adapted to the cooling requirements. The caulking of the screw provides for reliable fastening without damaging the material of the turbine blade. For a series of turbine blades which have approximately the same cooling requirements and the same internal construction of the cooling passages, a screw setting determined beforehand during an exemplary cooling-air measurement can be marked and set. The plug with the set screw is then inserted directly into the turbine blade and the screw is calked.